a/\(x^3-9x=0\Leftrightarrow x\left(x^2-9\right)=0\Leftrightarrow x\left(x-3\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x=3\\x=-3\end{array}\right.\)
b/ \(\left(5-2x\right)\left(2x+7\right)=4x^2-25\Leftrightarrow\left(5-2x\right)\left(2x+7\right)=\left(2x-5\right)\left(2x+5\right)\)
\(\Leftrightarrow\left(2x-5\right)\left(2x+5+2x+7\right)=0\Leftrightarrow\left(2x-5\right)\left(4x+12\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=\frac{5}{2}\\x=-3\end{array}\right.\)
\(x^3-9x=0\)
\(\Leftrightarrow x\left(x^2-9\right)=0\)
\(\Leftrightarrow x\left(x-3\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x-3=0\\x+3=0\end{array}\right.\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x=3\\x=-3\end{array}\right.\)
b ) \(\left(5-2x\right)\left(2x+7\right)=4x^2-25\)
\(\Leftrightarrow-\left(2x-5\right)\left(2x+7\right)-\left(2x-5\right)\left(2x+5\right)=0\)
\(\Leftrightarrow\left(2x-5\right)\left(-2x-7-2x-5\right)=0\)
\(\Leftrightarrow\left(2x-5\right)\left(-4x-12\right)=0\)
\(\Leftrightarrow-4\left(2x-5\right)\left(x+3\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}2x-5=0\\x+3=0\end{array}\right.\Leftrightarrow\left[\begin{array}{nghiempt}x=\frac{5}{2}\\x=-3\end{array}\right.\)
x^3 - 9x = 0
x(x^2 - 9) = 0
x = 0 hoặc x^2 - 9 = 0
x = 0 hoặc x^2 - 3^2 = 0
x = 0 hoặc x - 3 = 0 hoặc x + 3 = 0
vậy x = 0 hoặc x = 3 hoặc x= -3
a)x3-9x=0
=>x(x2-9)=0
=>x(x2-32)=0
=>x(x-3)(x+3)=0
=>x=0 hoặc x=3 hoặc x=-3
b)(5-2x)(2x+7)=4x2-25
=>-4x2-4x+35=4x2-25
=>-8x2-4x+60=0
=>-4(2x2+x-15)=0
=>2x2+x-15=0
=>2x2-5x+6x-15=0
=>x(2x-5)+3(2x-5)
=>(x+3)(2x-5)=0
=>x=-3 hoặc x=5/2
